Remove unused EXPECTED_SCHEMA_VERSION constant

Summary: This didn't end up getting used but I neglected to delete it.
Test Plan: git grep
Reviewed By: jungejason
Reviewers: tuomaspelkonen, jungejason, aran
CC: aran, jungejason
Differential Revision: 721

src/infrastructure/setup/PhabricatorSetup.php

@@ -18,8 +18,6 @@
 
 class PhabricatorSetup {
 
-  const EXPECTED_SCHEMA_VERSION = 36;
-
   public static function runSetup() {
     header("Content-Type: text/plain");
     self::write("PHABRICATOR SETUP\n\n");